The present invention relates generally to combustion turbine engines, and more particularly, to using fuel gas to purge dormant fuel gas circuits within a combustion turbine engine as the engine transitions through different combustion modes.
A combustion turbine engine, such as a gas turbine engine that releases low-level emissions of oxides of nitrogen (NOx), operates generally by staging the delivery of fuel gas to different fuel gas circuits (e.g., the fuel lines, fuel passage manifolds and fuel nozzles, etc.) within the combustor section of the engine as load is ramped up. Each fuel gas circuit utilizes a gas control valve to control the delivery of the fuel gas that is necessary for the circuit to receive during the various combustion modes that can occur during steady-state and transient-state operations. During certain combustion modes, some of the fuel gas circuits will have no fuel delivered. When the fuel gas circuits have no fuel delivered they become dormant during that particular combustion mode. While the fuel gas circuits are dormant, it is necessary to purge these stagnant passages in order to prevent condensate from accumulating, and to minimize the potential for combustion gases from back-flowing, which can result in damage to the fuel nozzles. Typically, the dormant fuel gas circuits are purged with high temperature, high pressure, purge air extracted from the compressor section of the gas turbine engine. After being purged with the air extracted from the compressor section, the fuel gas circuits wait in the dormant state until the combustion mode transitions to another mode that causes them to become active and have fuel gas delivered. When purging a dormant fuel gas circuit with purge air, there is a potential for creating a combustible mixture when fuel gas leaks across a closed gas control valve that is in flow communication with the circuit, and mixes with the purge air.